A magnetic disk apparatus as an example of a disk apparatus incorporates a magnetic disk in a case, a spindle motor which supports and rotates the magnetic disk, and a magnetic head for reading/writing data from/to the magnetic disk.
In recent years, a magnetic head employing a microwave assist recording system is proposed for the purpose of improving recording density, in which a spin-torque oscillator is provided as a microwave oscillator near the main magnetic pole of the magnetic head and a high-frequency magnetic field is applied from the spin-torque oscillator to the magnetic recording layer of the magnetic disk. Furthermore, a magnetic disk apparatus employing a drive control system is proposed, in which a drive signal in a first level, which is a fixed or steady level, is continuously supplied to the spin-torque oscillator, and a drive signal in a second level, which is higher than the first level, is supplied to the spin-torque oscillator for a predetermined time after the recording signal has reversed in polarity.
However, it may happen that a high voltage should be unexpectedly applied to the spin-torque oscillator due to switching noises or the like while making rapid changes between a drive signal of the first level and a drive signal of the second level, causing the oscillations of the spin-torque oscillator to be unstable. In the worst case, the spin-torque oscillator will be damaged.